I was buying the line 24 snap kits for $10 each, and here is what I learned:
You can get bags of 100 snaps relatively cheap. Brass is particularly cheap, but looks really nice.
Once you have the snap anvil and setter, setting the snaps by hand is relatively easy with practice.
A couple good, solid hits with a light rubber-headed hammer will do the job.
Line 24 snaps are for 5-7 ounce leather, which is roughly 2 to 2.75mm thick.
If the leather is TOO THICK, the snaps won't form or hold properly.
If the leather is TOO THIN, you will deform the snaps trying to get them together.
Different snaps are meant for different thicknesses of leather.
I use a 1/2-ton hand press (dirt cheap, $40) and the snap die and setter from one of the kits.
It's quicker than the hammer and less noisy for my downstairs neighbor
You can measure thickness with a pocket caliper like this one:
Home Depot Store SKU # 501570
(Needs lubrication, I suggest any except WD-40)
Reducing the thickness of leather is called skiving.
The Tandy super skiver requires practice to use, but it's $10.
A round knife can be used to skive, but it requires a LOT of practice and sharpening skills.
(That's where I am at, trying to learn how to use it).
I am still new to this hobby, I hope that my tips help you.
Relly